Name: Burning Iron in Liquid Oxygen - Periodic Table of Videos
Uploaded: 2020-03-27T18:12:08.000Z
Duration: 8 min 56 s
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Adverbs of degree

Sometimes Brady and Neil do experiments that are just for fun

So the experiment they decided to do was to

by putting it across the terminals of a small battery

and it glows red and you can see it burning in the air.

Not very vigorously but enough to stay red.

And then they dropped it into Neil's favourite cauldron

When they dropped it in, and they did it several times,

It didn't all burn because at the end there were

There are three oxides of iron: FeO, Fe₂O₃, and Fe₃O₄.

Heaven knows which one was formed in these reactions, and it was probably a ghastly mixture of them

but the formation of all of these is highly exothermic:

So you have iron going into the liquid oxygen

producing a lot of heat, and, because it's so hot, it produces a lot of light.

In essence, what was happening is that you have small pieces of very hot iron

A reaction like this is not very reproducible

because it depends exactly where you drop it, how the light is reflected,

where Brady was standing when he took the shot

so every picture is different, and nearly all of them are really beautiful.

Liquid oxygen is at a low temperature, -186 degrees centigrade

and you're dropping in a piece of hot metal

and you would expect that metal to cool down

The obvious interpretation, if you see these pictures,

is that somehow the iron is burning in this really cold liquid

but that's a contradiction.  How can something be very hot

Now, what I thought was that the iron was so hot that

it was effectively in a bubble of oxygen gas

But you can't really see that from the top

because you're looking through liquid oxygen.

So we decided we needed to do another experiment

so you could see the liquid and at the same time you could see the iron at the bottom

The first problem is that liquid oxygen is very cold

which can condense and ice the whole thing up very quickly.

You could get round this by using a transparent Dewar flask,

but they're quite expensive and the last thing you want to do

is to put hot metal inside it and crack your favourite Thermos vessel

and because these are evacuated, if they do crack,

but is unfortunate if it's an expensive piece of kit.

So, after discussion with Neil, we decided that the best thing to do

and try and fill the box with either oxygen or nitrogen

The experiment was moderately successful.

What I was hoping to see was the iron going in, sitting on the bottom,

Of course, what happened is that when it went in,

though Brady used some quite good tricks to get round this

and we couldn't get rid of all the ice forming

but the other thing, which we hadn't thought about,

that burning bits of iron were pushed out of the beaker pretty quickly

and they landed on Neil's favourite plastic box

but it was the silicone sealant which caught fire.

I didn't think that silicone burnt very much at all

but when you see what happened to Neil's box,

we had demonstrated beyond doubt that when you have an atmosphere of oxygen,

And I'm sad to say that Neil's box may be ruined.

But what was particularly surprising to me

that it had actually gone through the glass of the beaker

and effectively punched a hole through it.

we also found lumps of iron in the bottom

because the molten iron was hot and started forming larger lumps

and these larger lumps have a smaller surface area,

and eventually they cool down and the reaction stops.